The present invention relates to an oil-coated surface adhesive energy curable sealant composition having satisfactory adhesion to oil-coated steel sheets.
More particularly, the present invention is concerned with a sealant composition curable with energy, such as light or heat, which is advantageous not only in that the composition generates less odor during production, application, and curing of the products, but also in that the composition cured is strongly bonded to various materials coated with oil and it has excellent low-temperature flexibility.
In the production process for body of automobile, a great amount of a sealant is currently used for prevention of rust or corrosion. A body of automobile is generally produced by a process in which a cold-rolled steel sheet, galvanized steel sheet, or aluminum alloy coated with press oil or anticorrosive oil is pressed and then subjected to degreasing step (cleaning of oil) and electrodeposition coating, and a sealant is applied to the electrodeposition-coated surface of the sheet and dried, followed by application of intermediate coat and top coat. If possible, a sealant may be applied to the sheet and dried prior to the degreasing step.
Further, in the production process for precoated metal (precoated steel sheet), cold-rolled steel sheets, galvanized steel sheets, or aluminum alloy coated with press oil or anticorrosive oil must be cleaned to remove the press oil or anticorrosive oil. In the cleaning step, cleaning water and chemicals (additives, e.g., a surfactant) are used and hence a drying step and a wastewater treatment step are needed.
Sealants used for preventing automobiles from suffering rust or corrosion include vinyl chloride ones and urethane ones, but most of the sealants are vinyl chloride ones, which comprise polyvinyl chloride impregnated with a plasticizer and a stabilizer.
The vinyl chloride sealer contains chlorine and therefore has a problem that it cannot be disposed of with ease by burning. On the other hand, the urethane sealer is of a two-part type or moisture-curing type and hence it has a drawback that mixing by means of a mixing machine is required before application or it takes a prolonged time to set the sealer. Further, these sealers have poor adhesion to cold-rolled steel sheets, galvanized steel sheets, or aluminum alloy coated with press oil or anticorrosive oil and therefore, they may be washed away in the oil cleaning step before the coating step.
As a method for solving the above problems, in Japanese Patent Application No. 223978/1999, the present inventors already have proposed a photocuring sealant composition having excellent adhesion to oil-coated surface, using an acrylate monomer having a solubility parameter (SP value) of 9 to 14, filler, such as hydrophobic silica, and a phosphoric acid ester monomer. Specific examples of acrylates that the present inventors have proposed as a main component include 2-hydroxy-3-phenoxypropyl acrylate, 2-acryloyloxyethyl-2-hydroxyethyl phthalate, and phenoxyethyl acryalte.
However, the cured product of the photocuring sealant composition using the above acrylate monomer has a problem that the cured product has poor low-temperature flexibility and the monomer produces odor or fumes. Strong odor or large amounts of fumes cause the environment for production and curing (UV radiation) of the products to be bad, making it difficult to use the composition. Especially in the curing (UV radiation), investment of exhaust equipment is needed. For solving the problems, in the present inventions (1) to (9), it is an object to provide a photocuring sealant composition which is advantageous not only in that the composition generates less odor during production, application, and curing of the products, but also in that the composition cured is strongly bonded to various materials coated with oil and it has excellent low-temperature flexibility.
The sealant composition which is crosslinked and cured solely by a photoreaction has no problem in common uses, but when a current flows through the sealant composition applied to various materials in the electrodeposition coating step, the composition cured encounters a problem in that small bubbles generate between the sealant and the base material (especially an aluminum sheet or steel sheet). Further, there also occurs a problem in that the sealant cured may have only an unsatisfactory hardness. For solving the problems, in the present inventions (10) and (11), it is an object to provide a photocuring or thermosetting sealant composition which is advantageous not only in that the composition generates less odor during production, application, and curing of the products, but also in that the composition cured is strongly bonded to various materials coated with oil and it has excellent low-temperature flexibility and does not generate bubbles in the electrodeposition coating step.
Furthermore, as a photocuring sealant composition having excellent adhesion to oil-coated surface and requiring no cleaning step for oil, there has been proposed the above-mentioned sealant composition which comprises (a)an (meth)acrylate monomer having a solubility parameter of 9 to 14, hydrophobic silica as filler, and a phosphoric acid ester monomer. This composition proposed contains hydrophobic silica as an essential component in the monomer component to improve the oil absorption and the viscosity as a property of the sealant, and the operability (causing neither stringness nor sag) as well as the hardness of the sealant cured. However, the adhesion to oil-coated surfaces is required not only in the field of sealant but also in the field of coating agent. Thus, in the present inventions (13) to (15), it is an object to provide a composition having a lower viscosity than the high viscosity of the composition for sealant.